He stated this in Abuja on Tuesday, October 4, when he received Letters of Credence from the Ambassadors of the Republic of Tunisia, Mr Jalel Trabelsi and Federal Republic of Germany, Dr Bernhard Stephen Schlagheck.
Ambassador of Kingdom of Sweden, Mrs Inger Ultvedt and the High Commissioner of Canada, Mr Christopher Thornley, also submitted their Letters of Credence to the president.
In a statement issued by his Special Adviser on Media and Publicity, Mr Femi Adesina, the President said countries must be alert at all times and open to share information on activities of terrorists.
Following the G-7 meeting in Germany in 2015, Buhari disclosed that several countries offered their support to Nigeria in the fight against Boko Haram in the North-East.
According to him, the support made the degrading of Boko Haram possible.
He said: "The terrorists are all over the place and we must be more watchful.
"If a developed country like France can be attacked by terrorists to the point of killing about 130 people, then what more of developing countries.
"We need to build and keep increasing our capacities to network and stay ahead.
"We need to build these capacities across borders because terrorists operate across borders."
He added that the rehabilitation of Internally Displaced Persons (IDP) in the North-East also received attention from some countries, which provided services and materials to alleviate the humanitarian crisis in the zone.